How to turn on the PC without using the power button

Is there a way to turn on / off a DELL DIMENSION PC without using the power button? We integrate such PCs into information kiosks, so the PC box is completely hidden into the kiosk's box. We have to find a way to turn it on / off without having to open the kiosk body. Is there a way to configure Windows or the BIOS so that when we use the "shutdown" optin of Win XP, the PC does not completely turns off, but just shuts down the operating system. Thas ways, we could use an eletric switch to make the hardware switch off /on externally.